Star forming mystery Star formation in the early universe was far less efficient than it is now, confirms new research.

Based on observations of the star-producing power of two nearby galaxies, the study offers astronomers a fresh insight into the early Universe.

"We believe this is the first observational evidence to confirm theoretical predictions that star formation was not as efficient in early galaxies compared to spiral galaxies such as our Milky Way," says the study's lead author Dr Yong Shi of the Nanjing University in China.

Understanding how stars formed in the first galaxies is one of the key challenges of modern astrophysics.

Stars are formed through the collapse of cold dense clouds of molecular gas and dust. Heavy elements are needed to cool the molecular clouds sufficiently to create the right conditions for star formation.

"Theoretical models tell us the heavy elements can cool the gas helping it to collapse and form stars," says Shi.

"Once gas contracts it heats up and for the gas to further contract that heat needs to be removed. Dust grains and other molecules such as carbon dioxide are the main materials to help cool the gas."

However, in the early universe these molecular clouds were mostly hydrogen and helium - with very low concentrations of the heavy elements needed to cool them enough for stars to form.

This is because only hydrogen, helium and lithium were produced in the Big Bang 13.8 billion years ago - all the heavier elements were made by stars, through nuclear fusion, or when they die in supernova explosions.

Two galaxies

Shi and colleagues wanted to understand how well stars could be formed without these heavy elements needed to cool the molecular gas.

They used the Herschel Space Telescope to study two galaxies which are almost devoid of heavy elements, making them good chemical analogues for the primordial galaxies of the early universe.

One of the galaxies Shi and colleagues examined was a dwarf irregular galaxy named Sextans A, some 4.3 million light-years away, while the second was a blue low-surface-brightness galaxy named ESO 146-G14, about 72 million light-years away.

"We found that none of the star forming clumps identified in these galaxies were very efficient in making stars," says Shi.

The authors also saw far more infrared light than expected from these galaxies, indicating that there may be more molecular gas and dust than existing theories predict.